Derivatives of dialkyl-cysteines and allied compounds



N. ERCOLI Sept. 9, 1969 DERIVATIVES OF DIALKYL-CYSTEINES AND ALLIED COMPOUNDS Filed June '7. 1965 ww qs aso@ 7VH137 United States Patent O 3,466,312 DERIVATIVES OF DIALKYL-CYSTEINES AND ALLIED COMPOUNDS Nicholas Ercoli, Caracas, Venezuela, assignor to A. H. Robins Company, Incorporated, Richmond, Va., a corporation of Virginia Filed June 7, 1965, Ser. No. 461,855 lClaims priority, application Great Britain, June 8, 1964, 23,659/64; Sept. 4, 1964, 36,319/64 Int. Cl. C07f 9/76, 15/02, 9/94 U.S. Cl. 260-440 11 Claims ABSTRACT OF THE DISCLOSURE Compounds and chelates formed by the reaction of ,dialkylcysteines with organometallic compounds and metallic salts, wherein the metals are arsenic, antimony, bismuth and iron are described. The compounds and chelates reduce the toxicity of the metallic compounds without substantially impairing the therapeutic effectiveness of the metallic radical, thus greatly increasing the therapeutic index.

has been introduced as an eifective agent against poisoning with arsenic, antimony and mercury compounds. However the use of mixtures or complexes of these thiol compounds with metal containing preparations for therapy have not hitherto been practicable, since the therapeutic activity is also inhibited and the metallic `compounds are not only detoxiiied but also deactivated.

The action of the above mentioned compounds as agents against metal poisoning appears to be related to their activity as metal binding agents, due to the ability of the sulphur atoms they contain to form coordinate bonds with metal, particularly heavy metal, atoms, and in particular to the formation of chelates in which interaction between the metallic compound concerned and the thiol compound results in the incorporation of the metal atom into a heterocyclic ring containing at least one coordinate bond to the metal atom.

I have discovered that ,dialky1 cysteines of the formula (wherein R1 and R2=CH3 or C2H5), and to a lesser ex- 3,466,312 Patented Sept. 9, 1969 ICC tent their acetyl derivatives, reduce the toxicity of metallic compounds, while not substantially impairing the therapeutic effectiveness of the metallic radical. This is particularly surprising since related thiol antidotes, such as cysteine and dimercaptosuccinate so not have the same eiect.

This improved therapeutic index both increases the patients tolerance of therapeutically elfective metallic compounds, while reducing side elects, and permits a larger amount of a therapeutic preparation containing metallic compounds to be administered thereby improving its therapeutic effectiveness.

I have found that the reaction of dialkylcysteines, or analogues of dialkylcysteines in which the sulphur atom is replaced by selenium or tellurium, with metallic compounds produces compounds, complexes, or compoundcomplexes, generally chelates, of low toxicity, many of which possess therapeutic activity. It is well known that certain metallic radicals, such as antimony (trivalent or pentavalent) are eifective antiparasitic agents. Their usefulness is however limited in that they must often be used in the form of compounds of a relatively high toxicity. I have found that dialkylcysteine derivatives containing antimony are eifective antiparasitic agents of low toxicity, and it is believed that the dialkylcysteine radical increases the penetration of the metallic radical into the parasite, at the same time facilitating its elimination from the host.

Likewise, dialkylcysteine derivatives of other metals and organo metallic compounds provide a method of introducing these metals and compounds into a patient in an effective and relatively non toxic form, the dialkylcysteine radical improving the availability of the metallic radical and at the same time assisting in its elimination from the patient.

Accordingly, the invention relates to novel metal and organo metallic derivatives of dialkylcysteines and related compounds having the following general formula or their acid salts, where y is 0 or ,an integer less than or equal to v-x where v is the valency of the metal, z is 0 (except when y is 0) or an integer less than or equal to w-y, where w is the maximum number of coordinate bonds which can be formed with the metal, x is 0 or an integer up to v, Me is antimony (trivalent or pentavalent) arsenic, bismuth, iron (divalent or trivalent), selenium, or tellurium, or mercury, A is an organic or inorganic radical or radicals or where x is two or more, the remainder of a heterocyclic ring in which Me is included, R1 and R2 are -CH3 or -C2H5 and R3 is H or -CO.CH3.

The invention extends to a method of preparing the above derivatives by reacting a metallic or organo metallic compound of the formula AX.Me.Bu, where B is an inorganic radical or radicals and u is x-v, or when x=v, 0, with a dialkylcysteine or analogue thereof of the formula XH N HR:

or hydrohalide thereof.

The invention also extends to pharmaceutical products including one or more of the above derivatives or capable of forming such derivatives in solution. The reaction between the metallic starting compound and the dialkylcysteine or analogue may be of one or both of two types. Firstly, a condensation reaction may take place with the elimination of the hydrogen atom from the thiol or analogous group in the dialkylcysteine or analogue and an anion bonded to the metal in the metallic compound, a direct covalent linkage being established between the metal radical and the sulphur, selenium or tellurium atom in the dialkylcysteine or analogue. At the same time a coordinate bond is formed between the nitrogen atom in the latter compound and the metal atom. Secondly, and alternatively or additionally, a wholly coordinate linkage may be established between the metal atom and the sulphur, selenium or tellurium atom and the nitrogen atom in a dialkylcysteine or analogous molecule.

The derivatives may be prepared by mixing an appropriate metal oxide or halide, or a hydrohalide of an appropriate organo metallic compound, suspended or dissolved in water, alcohol, glycerol or other suitable polar solvent with the selected dialkylcysteine or diakylcysteine analogue. Condensation compounds formed may be separated if desired by adding ether, acetone or other organic liquid in which the product is insoluble.

A variation of this method consists in dissolving in alkaline solution stoichiometric amounts of a metallic salt and the dialkylcysteine or dialkycysteine analogue, and then if desired isolating the reaction product with ether or the like, as above.

An alternative method consists in the electrolysis of an inorganic salt of the desired metal dissolved in a solution containing water along with the dialkylcysteine or dialkylcysteine analogue: the metal ions will enter into a condensation reaction with the dialkylcysteine or dialkylcysteine analogue, the product then being isolated if desired. Both racemic and dextro rotary dialkylcysteines may be used for the synthesis, the dextro forms providing compounds of greater therapeutic index.

The invention is particularly applicable to compounds of arsenic, antimony, and bismuth containing an organic group or groups. Preferably, the ratio of the metallic compound to the dialkylcysteine ligand is adjusted to provide the greatest increase in therapeutic index. The resulting compound or complex may be utilized in the form of mixtures, solutions, and/or products obtained by the precipitation of solutions of the constituent compounds.

The unexpected therapeutic efficiency of the products of the invention is illustrated by the following experimentally obtained information. A lethal dose (LDQO) of 3-amino 4- hydroxyphenylarsenoxide (arsenoxide) reacted according to the invention with the same amount of dimethylcysteine is completely detoxified (in each case 50 mg./kg. given subcutaneously to mice). On the other hand, the therapeutic activity of the minimal effective dose of arsenoxide which induces disappearance of the parasites from the blood stream of mice infected with trypanosomes (T. equperdum), namely 1-3 mg./kg. maintains its effectiveness when used after reaction with the same quantity of dimethylcysteine, and even with such excess quantities as 100-200 mg./kg. dimethylcysteine. It is characteristic of the specificity of this observation that under similar conditions, other thiol antidotes of arsenic poisoning, as BAL, act in the opposite manner; that is to say they abolish more promptly the therapeutic than the toxic action of arsenoxide; to detoxify Mapharsan (arsenoxide), 1.0-2.7 times more BAL than Mapharsan is'required, while the curative effect disappears with doses of BAL as small as l to 1/2 of the Mapharsan weight (Ercoli and Wilson. Jour. Pharmacol. and Experim. Therapeutic 92: 121-126. 1948). Therefore, mixtures of BAL or BAL glycoside with arsenicals or antimonials are not therapeutically useful.

Thus the dimethylcysteine or ethyl-methyl-cysteine substitution of the oxygen or chlorine atoms of aromatic arsenoxides or dichlorarsines (Aryl-AsO; Aryl-AsClZ) increases their therapeutic index by decreasing their toxicity, while maintaining or improving the effectiveness of known effective preparations. Other therapeutically insignificant substituted aryl compounds assume useful properties by the introduction of this new As-:R2 radical (where R is a dialkylcysteine radical).

This substitution is particularly advantageous for 3- acetamino-4-hydroxy-arsinoxide to obtain a product of low toxicity for the treatment of amoebiasis and for -arsenobenzamide to obtain an antifilarial drug with better therapeutic index.

Analogously to the arsenicals, I have discovered that dimethyl or -ethyl--methylcysteine detoxifes organic antimony preparations (e.g. antimony alkali tartrates, antimony gluconate) when reacted therewith without interfering with their therapeutic efficiency. A similar effect was noted when using the N-acetyl derivatives of these dialkylcysteines, though to a lower degree.

In contrast, it is known (Chen et al. Jour., Infections Diseases. 76: 152-154. 1945) that cysteine itself reduces toxicity to the same extent as the antiparasitic effect of the antimonials. Thus, its positive antidotal action becomes counterbalanced by its negative effect on therapeutic efficiency and the combined treatment is not practicable. Similar results were obtained with a number of other antidotes of metal poisoning containing -SH and -NH- groups (benzoylamino--dimethyl acrylic thiol acid and a-benzoylamino--mercapto isovaleric thiol acid) structurally close to the dialkylcysteines (Ercoli et al. Archiv. Internat. Pharmacodyn. 136: 452-462. 1962). In the studies conducted in connection with the present application, it has been established that the antiparasitic action of 10 mg./kg. antimony potassium tartrate (against Trypanosoma eqzlz'perdum.) is destroyed by 0.7 mole, or less, of sodium dimercaptosuccinate, while 35 moles or more of d. or dl. dimethylcysteine did not affect it. Dimethylcysteine acetonide proved ineffective in changing the therapeutic index. The specificity of this invention for the specified dialkylcysteines is further confirmed as far as antihelmintic action is concerned by the reports (O. D. Standen in Experimental Chemotherapy. I. Schnitzer and Hawking. Academic Press, New York, London, 1963) that antimonyl tartrate is detoxified as much as deactivated by dimercaptosuccinate and other dithiols.

The high toxicity of selenium, which given as selenite in microgram doses prevents liver necrosis and bound to certain organic radicals is cytostatic, is reduced when it takes the place of sulphur in the above formula. In this form, the Me-Se linkage induces a reverse detoxification, namely the relatively much more toxic Se (or Te) is detoxified by the metal binding and can be used as cytostatic or antinecrotic agent.

The derivatives of the invention are illustrated by the accompanying examples:

Example 1 One part of potassium antimonyl tartrate (tartar emetic) is mixed with 1.5 or 2 parts of dl. dimethylcysteine or d. dimethylcysteine hydrochloride in powder form, and is heat sterilized and vialed as dry powder, which is stable over a period of years. The product obtained is soluble up to 6.15% in bidistilled water; the 5-6% solution indicated for treatment has a pH of ca. 6.4.

Besides the decrease of the general toxic effect of the antimony radical in this preparation, the local necrotizing effect of the tartar emetic disappeared also, in such a manner that the product can be injected intramuscularly (while tartar emetic can be given intravenously only), with the obvious advantages of this property for mass therapy. The therapeutic, and biological properties of two preparations containing 1 part of tartar emetic and respectively 1.5 parts (referred to as TPlS) and 2 parts (referred to as TP2) of dl. dimethylcysteine are illustrated in Table 1.

6 and molecular weight 440.04, together with 0.8 part excess dimethylcysteine, corresponding to a 2.4 fold molar excess of the dimethylcysteine, which forms a complex TABLE I Toxicity in mg./kg. Sb Therapeutic dose in Theratrypanosomiasis Schistopeutic LD50 Rabbit Sb, mg./kg. Indices somieidal index in mouse tolerated Irrltatmg dose Sb, Schistosubcut. intrav. Dog action Clarifying Curative Clarifying Curative nig/kg. somiasis Preparation K-antitmmyltartrate (tartar 18 3.6 5. 75 1 High, 0.1% 2. 65 11 6.7 1. 7 7.3 1. 8

110 None, 5%.. 4.1 20.4 27 5. 3 41 2. 7 51 8.6 (tex.) None, 6% 1. 8 10. 1 28 4 7. 5 6.8 83. 5 8. 4 28 i.m.1 None, 6% 1 8 10.1 46. 5 7. 8 8. 8 9. 5

In daily doses of 1.2-2.8 Inga/kg.

While there is an optimum proportion between the l5 metal-organic compound and the dialkylcysteine to obtain the highest therapeutic index, these proportions may be varied over a broader range as illustrated by FIG. 1 (in the case of tartar emetic and dl. dimethylcysteine the optimal ratio is 1:4 molar). Among other changes in bio- L) logical properties, the direct antiparasitic activity of the antimonial has been also increased to a considerable eX- tent in the solution with the dialkyl cysteine. Cercariae of the Schz'stesoma mansoni exposed to tartar emetic were immobolized within 3 hours when exposed to 10-6 moles in the solution containing 2 parts dl. dimethylcysteine (TF2 of Table l), while alone a much higher concentration (1/70000 mole) of emetic gave this eiect only after 5 hours. Similarly, the tripanocidal activity has been increased 2 to 3 fold taking as criterion of comparison both the immobilization and destruction of the parasites. (This potentiating effect is due presumably to a greater penetration of the parasite of the product formed in the solution with dialkylcysteines.) An identical procedure for preparation can be used, replacing antimonyl tartrate with sodium antimonyl glyconate (Tristam).

Example 2 One part of sodium antimonyl tartrate is mixed with 1.66 parts of dl. dimethylcysteine and is heat sterilized and vialed as dry powder, as in Example 1. The resulting complex-compound, containing 14.9% Sb, had an LD50, given subcutaneously to mice, corresponding to 82-110 Ing/kg. Sb, in comparison to 8-10 mg./kg. Sb for the sodium antimonyl tartrate used for its preparation. Thus, the degree of detoxification is considerably higher than in the previous example (TP and TF2), reaching a toxicity decrease in the order of 1:10. This highly detoxified complex compound has been used clinically, under the name of NaP, for intensive treatment (short term therapy over 5-8 days) of bilharzia patients. The patients received one intramuscular injection for ve consecutive days of 400 mg. NaP injected intramuscularly in 5 ml. bidistilled Water. The injections were painless and well tolerated. The curative results obtained were the highest reached so far in the treatment of this disease, 87% clearing rate of bilharzia patients observed for a period of 3-6 months for egg elimination. The comparative results with other drugs obtained in the same Bilharzia Service Centre as far as tolerance and therapeutic effect are contained in Table Il.

This preparation (NaP) given orally to man in enterocoated pills or capsules was well tolerated in daily doses corresponding to about 100 mg. Sb, the highest tested so far.

The preparation (NaP) comprises the compound sodium antimonyl-dimethylcysteinyl tartrate having the probable structure.

TABLE II Clinical Efficiency, Drug Percent Intolerance Fuadin (Stibophen) 46 -I- 1 Astiban (500 mg. Sb total) 71 -l- -l- -l- Anthiomalin 30 -i- -i- TF2 (200 mg. Sb t0tal) 51 =l=2 NAP (298 mg. Sb total) l Cases of lethal toxicity. 2 Almost nil.

The statistics on TP2 and NaP are based on 220 Bilharzia cases, while the other data on Fuadin and Anthiomalin are the result of about 2O years of experience of the Centre on thousands of patients. Astiban has been tested by Dr. Ron Pedrique and coworkers on cases.

Example 3 One gram of K-antimonyl tartrate and 1.5 grams of dl. dimethylcysteine are dissolved in 40 cc. distilled water 40. The addition of 300 cc. of acetone or 400 cc. ethylalcohol forms a crystalline deposit with an Sb content of 14-15 and a LD50 corresponding to 40-50 Ing/kg. Sb injected subcutaneously in mice (ca. 3 times that of antimonyl tartrate) with a curative index in trypanosomiasis 10C-150% higher than that of the Sb tartrate used for the preparation.

The Sb content of the crystalline preparations so obtained can be varied according to the ratio of antimonial and dialkylcysteine used, all having an increased therapeutic index in yrelation toxicity referred to Sb content.

l The optimal preparations for therapeutic use are those containing l0 to 20% Sb, obtained fby the method described from the original organic compounds containing 36 to 39.5% Sb (antimony potassium tartrate 36.5%: antimony sodium tartrate 39.4%: sodium antimonyl gluconate 36% These materials are suitable for the preparation, purification and isolation of chemical compounds of defined structural formula containing Sb and two organic radicals, one of them the dialkylcysteine, the other re spectively tartaric or gluconic acid for example.

Example 4 (a) One gram of 3amino-4-hydroxyphenylarsenoxide (arsenoxide) was uniformly mixed with 2 grams of d. dimethylcysteine hydrochloride, 3.0 grams sucrose, 0.18 gram sodium carbonate and 0.03 gram ascorbic acid. The preparation was vialed to contain 60 mg. arsenoxide for single adult dose (162 mg. of the mixture), dissolved in distilled water before use. The LD50 for mice of the arsenoxide-dimethylcysteine derivative in the preparation was 150 mg./kg.: i.e. the preparation decreased 2.7 fold in toxicity with an activity identical to the starting product, which represents a corresponding I(2.7)() increase in safety. Improvement of the safety factor, to varying degrees, is obtained using 1 part arsenoxide and 0.5 to 6 parts of d. dimethylcysteine hydrochloride.

The lower toxicity of the product extends not only to the systemic but even to the local action of the arsenical, which in the form of the present composition can be utilized by intramuscular injection also. While arsenoxide caused severe necrotic lesions on rabbit skin in 1-2 mg./ml. concentrations (given intradermally), 20 nig/ml. of the arsenical in presence of the dialkylcysteine induced no lesions.

8 containing (calculated) As, 12.7%; C, 32.2%; N, 7.1%; S, 10.7%; H, 4.95%; O, 13.6%; Cl, 18%. I found: As, 12.08%; C, 29.75%; N, 6.6%; S10, 2%; H, 4.54%; O, 15.2%; Cl, 21.65%;

The minimal lethal dose of this compound for mice is 200 mg./kg., while it clarifies Tiypanosoma equipardum infection of the same species in 2.5-3.0 nig/kg. subcutaneous doses and induces permanent cure with 12. mg./kg. Compared to the corresponding arsenoso (-AsO) compound, Arsenoxide (Mapharside), the therapeutic index has been increased by not less than 100%. The improvement of the therapeutic index is even greater with the dextrorotatory compound.

The intramuscular use of arsenoxide practicable in the Example 5 form of the preparations here described permits the l combined treatment with other drugs in the fom Ot a Similar increases in therapeutic. indices occur using as single pharmaceutical preparation, without having to rest artmg @mel-ml for th? preparano 4'Carbanfyl'phenyl sort to two different routes of administration (eg. indlchlfrarsme to Obtffm P arsenosobenzamfde'd1a1k-yl' travenous for arsenoxide and intramuscular for penicil- 2O Cystemes or 3'acetalmn04'hydroxy'phenyldlchiorarslfe 1in) and p-ureido-phenyldichlorarsine for condensation with (b) Similar improved therapeutic products can bc ob the dialkylcysteine. As in the case of the antimonials, the tained using t part of 3 amin@4 hydroxyphenyldichloro dextro form of the selected dialkylcysteine will result in arsinc hydrochloride (dichlorphcnarsiuc) with 2 parts of the less toxic compound, with a higher therapeutic index. dl. dimethylcysteine. The subcutaneous tolerated dose of E l 6 dichlorphenarsine increased from 12 mg./kg. As to over Xamp e k .A bl 3 wh'le the tr anoc'd lactivit rmasinfe'auraltred and in iiiiro bcme eveii Arenarlde (4'carb-am1d0 RhenlfldlCafbOXy me'thylthiohi her, 009 /ml As in the form of dimeth 1c Steine arsenite) 1s an eicientantilarial' d rug, but'it 1s too rfi artion ir'gc'om arison to o 14 /ml A 05g dBi/Chlo? o toxic for general use (Brit. Med. Dictionary. Sir. Arthur rsle p Mg" s d Salisbury, Caxton Publishing Comp. London. 1961).

The therapeutic properties of the product can be ac- Ecient, products of reduced toxicity ae prepafed (a) counted by the formation in solution of 3-amino-4-hyby d1 S501Vmg 1"3 Paffs meflylehylfystelne or dimethyldroxyphcnttrsinodioimcthylcystcinc' This compound cysteine powder kept m sterile vials in a commercial 'soluhas a tolerated dose corresponding to 18 mg./kg. As, but 35 non 0f afsenamlde Just beffe I lse- A V131. Cont'llnlQg it has been further detoxied t0 35 ,ng/kg As (Table 160 mg. dl. dimethylcysteine is suitable for dissolution 1n B) by the presence of excess dl. dimethylcysteine which 6-8 CC- 1% arse-Hamid@ at PH 72 by all alternative method through coordination bonds with the As atom forms a consisting in the preparation of dry mixtures 0f the Sodicomplex of the new compound. urn salt of arsenamide, 80 mg. per vial with 150 mg. of

TABLE HI d1. dimethylcysteine to be dissolved before injection.

Toxicity of dichlorphenarsine alone and with dl. di- Example 7 methylcysteine compared with trichlorhydrate of 3-amino- 4-hydroxyphenarsine-di--dimethylcysteine One part of N-carbamylarsanilic acid (Carbarsone) is Total dose .As drug, No. No. content, mg./kg. mice mico Preparation percent subeutan. injected died 5o 12 0 Dichlorplienarsine 25,8 75 g g 100 1 part Dichlorphenarsine plus 1 part d1. 150 6 0 dimethylcysteiue 12.9 250 3 3 o 3 3 300 6 0 1 part Diclilorplienarsine plus 2 parts dl. 300 3 0 dimetliylcysteiue 8,65 i I 3-nn1ino4hydroxy plicnarsine-di-,di 150 4 2 methylcysteine.3HCl 12. 08{ ggg (c) Trichlorhydrate of 3-amino-4-hydroxy-phenarsinedi-,dimethy1cysteine (or 3-amino-4-hydroxy-phenylarsenide-DL--mercapto-valine). 2.2 grams Dls-dimethylcysteine contained in 9 ml. ethanol were slowly added to 2 grams of 3-amino-4-hydroxy-phenyldichlorarsine hydrochloride dissolved in 6 ml. ethanol. The mixture was heated by reuxing for 1 hour, the material remaining insoluble being removed by vacuum filtration. To the ltrate rst 10 ml. ethanol then 50 ml. chloroform were added, which induced the formation of a white precipitate. This was filtered, and desiccated in vacuo where it lost its resinous consistency and became a white-grayish powder. Dried to constant weight at 40 C. in vacuo it lost 4.4% weight. The analysis gave values corresponding to the formula:

mixed with 0.2 part calcium gluconate and 0.7 part of dl. dimethylcysteine. The composition is used in the form of capsules (500 mg.) for the treatment of amebiasis.

Example 8 Example 9 (a) One part of antimony trichloride is mixed with 2.4 parts dl. dimethylcysteine and 2 parts of sodium carbonate under careful conditions of dryness. The resulting snowy powder dissolves rapidly in water with libera- 9 tion of CO2. The solution of the mixture has a pH of 6.8 and can be injected without causing lesions. Its LD50 for mice (subcutaneous) corresponds to slightly over 100 mg./kg. Sb (Table 4).

The reaction which takes place by dissolving the mixwhite crystals melting with decomposition at 16S-170 C. were obtained. Analysis gave values corresponding to a monohydrochloride of the expected compound: SbCH30N3O6S3-HCl (M.W. 602.26). Theoretical values: Sb, 20.2%; C, 29.9%; H, 5.15%; N, 6.9%; O, 15.9%;

ture in water leads to the formation antimony-tris-dl- 5 S, 15.9%; Cl, 5.9%. The experimental values found were: @,-dimethylcysteine which has a lethall dose correspond- Sb, 19.5%; C, 31.68% (in other samples 29.43% and ing to nig/kg. Sb, but can be considerably increased 30.17%); H, 4.71% (4.91% and 5.01%) N, 6.37%; by the addition of 25-50% excess dl. dimethylcysteine O, 17.25%; S, 15.30% (15.9% and 15.62%); Cl, 5.48%. (Table 4). 10 In two of the three preparations analyzed, prepared In the mixture of the present example the theoretical with various modifications of the above method (reratio for the reaction between SbCl3 and dimethylcysteine flux heating instead of aufoclaving), the C1 values is 1.9, while an excess of 2.4 parts dialkylcysteine Was were lower (2,95% and 2,5%), which was dus to used, which accounts for the high tolerance 0f the new more prolonged washing of the wet trioxide leaving inproduct, since a complex 1s formed in the solution with 15 suicient HC1 to bind the whole of the free amine in the the excess dimethylcysteine. form of hydrochloride.

In this example it has been established that a COm- The lethal dose (LD) of the compound administered pound is formed which is further detoxified by the eX- subcutaneously to mice was 150 nig/kg., while the dose cess d1. diniethylcysteineentering into a complex with the Clearing a Trypanosoma equz'perdum. infection was 10 new compound formedin solution. The new compolmd- 20 ing/kg., i.e. 1/15 of the lethal dose. The toxicity of the comPlex 1S aHUmOPY-Ul-dl-idlmethylcystelne, With lS compound could be further decreased, to a LD56 of 400 Sb bQUIld by COOfdlIlae linkages t0 the eXCeSS dldimethyl' mg./ kg., while the therapeutic effect was fully maintained, cysfemeby adding 0.25 parts dimethylcysteine to one part of the Si; to a of 2r t l produce further detoxification (in fact, it reduced 1t), d mhsgsssteme the compound formmg a complex Wlth proving that the resulting toxicity and biological charac- Th 'd t t f d. 1k I teristic of the mixture in aqueous solution is determined e Pro uc s cfm ammg an emes? .o ia y systeme by the equilibrium between the new chemical structure are particularly suitable for oral administration, by counand the ligand dl. dimethylcysteine. Toxicity of antimony- 30 teractmg the tendency of the orgamc derlvatlves md of tris d1 8 dimethy1cysteine (Sb(DMC) 3) and its DLDithe chelates to decompose at the low pH of the gastric conmethylcysteine complexes compared to Preparation of tent. The treatment with antimonials tolerated and ab- (Example 9a) sorbed by the oral route, besides its obvious advantages TABLE IV Total dose Sb drug, No. content, mg./k mice No. Preparation percent subcutan. injected died 100 3 1 Sb (DMC)3 19. 5 150 3 1 20o-ggg d t4) 1 tsb DMC 1 0.25 td1. d' th 1- -13.21? rei .eil gg g g o-750 4 4 1 part Sb (DMC)3 plus 0.5 part dl. dimethyl- 250 4 0 cysteine 12.9 ggg 1 part Sb (DMC)3 plus 1 part dl. dmethyl- 300 4 0 cysteine 9. 25 500 4 0 600 8 7 Example 9a 300 2 0 1st sample: SbCla/dimethylcysteine, ratio 2.4.... 15. 5 1I 25 2 200 2 0 400 2 o 2nd sample: SbCls/dimethyleysteine, ratio 2.7..- 14. 6 1,000 8 7 Pretreatment with 200 mgJkg. dimethylcysteine subcutaneous followed by Sb (DMC)3 400 4 0 methyleysteine, without losing therapeutic effectiveness.

(b) Analogous preparations can be obtained with a mixture of antimony oxide and dialkylcysteines, however, these enter more slowly into solution and generally require heating.

(c) Twenty grams of SbCl3 were added to 100 ml. water to form a mass of 16 grams of wet trioxide (a mixture of Sb203 and hydrochloric acid). This mass was rapidly washed on a filter (with ca. 20 ml. water) then added to 100 ml. distilled water in which 10 grams DL- dimethylcysteine were dissolved. The mixture was heated in an autoclave at 120 F. and 15 lbs. pressure for 2 hours, reltered and the filtrate concentrated in vacuum to encourage the formation of crystals which were pH. This preparation (the free amine) has the same bioformed in a heavy mass on the addition of alcohol. By successive recrystallization from water-alcohol mixtures,

for mass therapy, leads also to relatively higher Sb coricentrations in the portal system where the schistosomes are localised in a S. mansoni infection.

(d) 9.34 grams DL dimethylcysteine were dissolved in ml. water in a 3-necked 500 ml. round bottomed flask and stirred, while N2 gas was passed into the, flask to minimise air oxidation. After 4.98 gm. NaOH had been added, 4.75 g. SbCl3 dissolved in 25 ml. absolute alcohol were added slowly from a dropping funnel; a precipitate appeared briefly, but immediately redissolved. Stirring was continued for 30 minutes and then the solution was refluxed on the Water bath for l hour. To the reaction mixture, concentrated in a flash evaporator to a small volume, dry alcohol was added. The precipitate was filtered, washed with alcohol and dried under vacuum. The product, a white solid, was readily soluble in water at neutral 1 1 logical characteristics as the mono-hydrochloride. In doses of 200 mg./kg. it killed 75% of the mice to which it was administered (i.e. its LD75 was 200 mg./kg.), while 12.5 mg./kg. cleared T rypanosoma equperdum` from all infected animals treated.

Example 10.-Antimony-D-dimethylcysteine hydrochloride (a) The reduced toxicity of the product of mixing antimony trioxide with d.dimethylcysteine hydrochloride was found to be due to the formation of antimony-d-dimethylcysteine-hydrochloride. The tolerance of this compound was the highest encountered, corresponding to an LD50 (mouse) of 245 mg./kg. Sb, with a favourable therapeutic index in trypanosomiasis, infected mice being cleared by 1/0 of the lethal dose, i.e., 25 ing/kg. of the preparation, corresponding to 6.2 mg./kg. Sb.

(b) One gram of d-dimethylcysteine hydrochloride was dissolved in ml. distilled water, and to this solution 1 gram of freshly precipitated (from SbCl3), wet Sb203 is added. The suspension was reuxed over a water bath for 3 hours. After filtration, it was concentrated by vacuum-centrifugation leaving an oily material; this was dissolved in ethyl alcohol and precipitated with ether. The white powder melted with decomposition at 168-170 C. Microanalysis gave values corresponding to the formula Found: C, 23%; Sb, 24.4%; H, 3.7%; N, 5.8%; O, 12.9%; S, 12.9%; Cl, 12.4%. Calculated: C, 24.5%; Sb, 24.7%; H, 4.4%; N, 5.7%; O, 13.0%; S, 13.0%; Cl, 14.6%.

Example 1l.-Mercury-d-dimethylcysteine hydrochloride Two grams of HgClZ were dissolved in 100 ml. distilled water and 16 ml. NaOH solution added. The insoluble HgO precipitated was repeatedly washed with distilled water on a filter, then resuspended in ml. distilled water. This suspension was slowly added to 60 ml. of a solution containing 1.5 grams d-dimethylcysteine hydrochloride heated at 70 C.; the mercury oxide immediately dissolved. The reaction product can be recrystallised by gradual cooling or recovered quantitatively by the addition of 2-3 volumes of a mixture of butyl alcohol and ether, or by adding ethyl alcohol. The white product precipitated by alcohol decomposed at 177-185 C., that precipitated by the butylalcohol-ether mixture at 180- 190 C., giving a peculiar characteristic odor which accompanies the decomposition of these metal-organic compounds, and a black residue of HgS.

Example l2.-Mercury -dldimethylcysteine hydrochloride 2.01 grams of HgCl2 were dissolved in 30 ml. absolute alcohol and 2.3 grams of DL. dimethylcysteine were sii-spended in 105 ml. of the same medium in an Erlenmeyer flask. The HgClz solution was heated on water bath while the alcoholic dimethylcysteine suspension was slowly added to it. The suspension went immediately into solution as a result of the reaction with the HgCl2. The reaction product could be collected by slow crystallization after cooling or by precipitation with ether. The white crystals formed, observed on a heated plate under the microscope, started to volatilize at 170 C. without melting; before the temperature reached 180 C. a black residue was formed. The compound was water soluble; on heating the solution became turbid, but the addition of NaOH clarified it. HgS was precipitated by the addition of H28 in acid solution. Its formula was Hg(SC5H10O2N.HCl)2 (Hg, 35.2%; H, 3.85%; C, 21.2%; S, 11.3%; Cl, 12.4%). Microanalysis gave the following 12 experimental values: Hg, 38.75%; H, 4.17%; C, 22.26%; S, 11.18%; Cl, 12.45%. The material, alone or in cornbination with dialkylcysteine, can be used as an antibacterial and/or diuretic agent.

Example l3.-Ferrous and ferric dand dl. dimethylcysteine (a) 1 gram ferrie sulphate was dissolved by heating in 200 ml. water and ferric oxide precipitated with 10` ml. 5% NH4.OH. The ferric oxide formed was washed until neutral on the filter, then suspended in 60 m1. water. To this suspension 600 mg. of DL-Cimethylcysteine hydrochloride (or the free amine) dissolved in 45 ml. water were added. The mixture on being heated to boiling for 10 minutes took on a dark violet colour; it was filtered and 100 ml. ethanol and 200 ml. ether were added to the filtrate. Two layers formed, the superior colourless, the inferior violet and containing the compound, and were separated. To the violet liquid ml. alcohol and 200 ml. ether were added, which induced the precipitation of the expected compound: Fe(C5H1NO2S)3 which had a brownish colour, was soluble in alkalis, and on neutralization was precipitated by HZS. It had a strong tendency to hydrolyze and to reform the insoluble Fe oxide.

(ib) 500 mg. FeSO4.7H2O (M.W. 278.03) were dissolved in 5 ml. glycerol and 550 mg. DL. dimethylcysteine (M.W. 151.18) in 15 ml. glycerol. A current of hydrogen was passed through the solutions before mixing them, whereupon the combined solution was saturated with NH3 until the initially violet colour turned to yellowish. From this solution, by adding a mixture of two volumes alcohol and 408 volumes ether, an oily yellow deposit was first obtained which by successive treatment gave a solid material comprising mainly the reaction product expected: Fe(C5H10NO2S)2. This product was water and alkali-soluble and was easily decomposed to give the insoluble oxide.

(c) On electrolysis in a U-tube of mg. FeSO4.7H2O and mg. DL. dimethylcysteine in 13 ml. glycerol to which l ml. water was added, at 0.5 ma. and 200 volts, the solution on the cathodic side became an intense violet colour. The violet solution collected from the cathodic side of the U-tube, precipitated with 2 volumes of alcohol and 5 of the ethyl-ether gave a bluish product, a mixture of the ferric and ferrous dimethylcysteine derivatives. This preparation was easily decomposed into the brownish oxide. (With proper precautions, maintaining a tight hydrogen chamber on this cathodic side of the tube it is possible to avoid the oxidation of the ferrous form.)

(d) Using dialkylcysteines soluble in organic solvents, for example D-dimethylcysteine hydrochloride, which is soluble in ethanol, a practical method of preparation consists in placing the dialkylcysteine over a layer of the same weight of ferrie hydroxide, freshly prepared as in Example 5a, but washed with alcohol after precipitation, in the extractor chamber of a Soxhlet apparatus. The alcohol vapour condensed in the chamber dissolves the dialkylcysteine and passing through the oxide, forms the reaction product, which drops continuously into the bottle generating the alcohol vapour. Under these conditions, a brownish product, soluble in water, is formed, which on heating decomposes leaving a black residue (FeS). Both the ferrous and ferric dialkylcysteine derivatives can be used as hematopoietic agents.

Selenium and tellurium derivatives of dialkylcysteines may be prepared by similar methods. It is believed that they may be effective as cytotoxic agents to inhibit excess cell growth.

Example 14 Further examples of dialkylcysteine derivatives of metallo-orgamc compounds are given below: Diphenylethylmethyl-chlorarsine te cm-otm-ornCHVAe-oi reacting with the dialkylcysteine gives an arylalkyl 13 (alkyl) (mono dialkylcysteine)arsine. The arylstibonous halides (ArSbCl2) or the aroxostibines (NH2C6H4-SbO) form di-dialkylcysteine compounds. Chlorodiphenylstibine (C6H5)2.SbCl forms a diaryl(mono)dialkylcysteine-stibine. Correspondingly, 2.ch1oro1,3 dithia-Z-arsacyclopentane CHT-S AsCl CH2-S forms a 2 dialkylcysteinyl-1,3dithia-2-arsacycl0pentane, as does the stibiacyclopentane derivative of dimercaptopropanol (BAL) in which 2 bonds of 3-valent Sb are linked in an internal dithiol ring, the third to the dialkylcysteine selected. Other heterocyclic organo-metallic compounds containing for example arsindole, 1,3-dithiaarsacyclopentane, 1,3-stibiacyclopentane, phenothiarsine, or dimercaptopropanol-cyclic-bismuth rings may also be used. Triphenylbismuth dichloride (C6H5)3BiCl2, gives a triaryl-bis (dia1ky1cysteine)Bi compound.

What is claimed is:

1. Alkali metal salts of antimonyl-dialkyl cysteinyl tartaric acids and complexes thereof with dialkyl cysteines.

2. Products of the reaction in aqueous solution of 4- carbamide phenyldicarboxy methyl thioarsenite with a dialkyl cysteine.

3. Products of the interaction in aqueous solution of N-carbamylarsanilic acid and an dialkyl cysteine.

4. Products of the interaction in aqueous solution of sodium bismuth thioglycollate and a dialkyl cysteine.

5. 2-dialkyl cysteine-1,3-dithia-2-arsacyclopentane.

6. 2 dialkyl cysteine 1,3 dithia 4 methylol 2- stibiacyclopentane.

7. Triaryl-bis-dialkyl cysteine-bismuth.

8. 2-dialkyl cysteine-1,3-dithia-4-methylol-2-bismuthylcyclopentane.

9. Alkali metal salts of antimonyldialkyl cysteinyl gluconic acid, and complexes thereof with dialkyl cysteines.

10. 4-carbamyl phenarsine-di--dialkylcysteine.

References Cited UNITED STATES PATENTS 3,297,531 1/ 1967 Friedheim 260-446 XR 1,672,615 6/ 1928 Kharasch 260-431 1,684,920 9/ 1928 Kharasch 260-446 2,559,061 7/1951 Banks et al. 260-440 2,701,812 2/ 1955 Takahashi et al 260440 3,002,985 10/ 1961 Imado 260-439 3,281,461 10/1966 Restiro 260-534 OTHER REFERENCES Public Health Report, vol. 54, No. 29, pp. 1320-1321 (1939).

Chemical A-bstracts, vol. 25, p. 740 (1931). Chemical Abstracts, Vol. 49, p. 118702. (1955). Chemical Abstracts, vol. 50, pp. 3134i-3135a (1956). Chemical Abstracts, vol. 50, p. 6234e (1956). Chemical Abstracts, vol. 55, p. 5467a (1961). Chemical Abstracts, vol. 57, p. 5578a (1962). Chemical Abstracts, v01. 54, p. 22131a (1960). Chemical Abstracts, vol. 53, p. 101811 (1959). Chemical Abstracts, vol. 24, p. 3991 (1930). Chemical Abstracts, vol. 29, p. 80175 (1935). Chemical Abstracts, vol. 41, p. 3758g59( 1947). Chemical Abstracts, vol. 49, p. 87246 (1955 Chemical Abstracts, vol. 50, p. 5038c (1956).

5 TOBIAS E. LEVOW, Primary Examiner H. M. S. SNEED, Assistant Examiner 

